This invention pertains to apparatus to support a drilling rig elevator, or spider, in the opening of a rotary table. Essentially, it makes a flush spider of a conventional elevator or spider.
On drilling rigs, the traveling block is usually equipped with bails that hang from ears on each side to suspend loads. The bails, in turn have eyes or loops at the lower end to engage ears or lugs, on pipe elevators that engage the top end of pipe strings to suspend them in wells. Elevators and spiders both grip pipe in much the same manner and may have identical pipe engaging contrivances. Spiders, however, usually remain on the rig floor and support pipe strings when the elevators are not raising or lowering the pipe string. Both elevators and spiders commonly have housing structure that can transfer the load of a suspended pipe string to lifting engagement means, on the housing, that transfer the load to a traveling block by way of bails or links. Lifting engagement means may be ears that engage bails, or lugs that engage links. Bails have loops and links have eyes to engage the lifting engagement means.
Elevators usually have a pipe guide funnel, or flange, on the bottom and that feature normally will not support a heavy pipe string load. If the flange fitted elevator is suspended in the rotary table by the structure of this invention the flange does not have to be removed to convert the elevator to a spider.
There is a need to reduce the height from the rig floor to the upper end of the pipe string where connections have to be worked. The joints are worked above the stack height of both elevator and spider. Suspending the spider into the rotary table opening can reduce the height of the connection above the rig floor.
If the opening in the rotary table is large enough to permit structure to suspend a floor plate in the opening, a spider can be installed in the opening to rest on the floor plate. That is a well-known practice. If the spider diameter is too near the diameter of the rotary table opening, there is no room for the suspension structure.
Spiders are known to have been used when supported on a movable plate that rested on the rig floor above the rotary table opening. That did nothing to lower the height, above the rig floor, of the pipe connection being worked by that arrangement.
There is a need to suspend a spider in the rotary table opening without using structure that interferes with activity above the rig floor. An elevator can be suspended in the rotary table opening and function as a spider.
A shaped plate, or comparably shaped structure capable of a bridging function, is provided on each side of the spider to replace the bails and transfer the pipe string load from the spider ears, or lugs, to the rig floor. At present, it is not advantageous to weld up the plate from an assortment of structural elements because solid plate is more economical. If lugs are to be engaged by the plate, there are cutouts, or openings, to accept the lugs and a cross channel in the plate to accept attachment means, preferably a pin. If the spider has ears, the cut-outs accept the pin ends of clevis"", or shackles, and the shackles swing through the opening below the ears much as did the loops on the bails. Like a clevis, the shackle has ends that are adjacent and provided with aligned holes, or eyes, for a closing pin. The eyes in the shackle receive the preferred horizontally extending pin in the cross channel. If solid plate is used, a simple cross bore can be drilled for the cross channel. It leaves a cleaner upper surface on the plate.
When pinned together, the two plates and the spider suspended below them form a composite package. The plates, collectively, have geometry that carries the pipe string load to the rig floor. A generally squared plan form is convenient and a structurally efficient shape for the paired plates. With the suspended spider in the opening of the rotary table the plates extend beyond the rotary table opening to bear upon the rig floor, or rotary table upper flange. The plates are shaped to leave a generally central opening to accept a vertical pipe string. With their thickness above the rig floor plane the preferred plate arrangement comprises a small, very stable, work platform.
The suspending structure can be the equivalent of a single composite structure if the supported spider is known to fit the attachment means. The paired plate arrangement is preferred because hinged spiders can be opened as much as is usually required of the spider while still attached to the suspending structure.
As a handling convenience, lifting eyes on the plates are situated over the cross channels, preferably cross bores, which are near the balance lines of the plates. Whether lifting just one plate or the assembly of plates and spider, parts lifted remain level and stable. This handling arrangement is not intended to lift a pipe string. This handling convenience is anticipated by the claims but is not to be construed in a limiting sense.
It is an object of this invention to provide bridging apparatus to suspend a spider in the opening of a rotary table to reduce the height of the upper end of a suspended pipe string when pipe sections are being added.
It is another object to provide apparatus to suspend a spider that has either lugs or ears for support in the rotary table opening; adding only shackles to change from a lug-type to an ear-type spider.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.
For the purpose of this application, the top of the rotary table and the adjacent load-bearing floor will be defined as the rig floor.
For the purpose of this application, support lugs and pad eyes on elevators and spiders are the same.